1. Field of the Invention
This invention relates to oscillator/amplifier circuits, and more particularly to microwave oscillator/amplifier circuits using at least one negative resistance device.
2. Prior Art
A negative resistance oscillator basically comprises a negative resistance device connected through a resonator, tuned to the desired frequency, to a load. The impedance presented by the cavity and load to the device is the negative of the negative resistance device. Typical examples of negative resistance devices used for generating microwave oscillations are the bipolar transistor, the field effect transistor, IMPATT diode, TRAPATT diode, Gunn diode, tunnel diode, LSA diode, etc. As is well known in the art, many negative resistance oscillators can be loaded to the point where oscillations will cease, where it will then produce reflection gain. With this overcoupled oscillator/amplifier is then used with some device to separate the incident power from the reflected power, such as a ferrite circulator, it can be used as an amplifier. In that sense, this invention pertains to both amplifiers and oscillators. However, for purposes of discussion, the invention is described in the oscillation mode. This is not meant to detract in any way from the invention's usefulness as an amplifier.
Prior art microwave negative resistance oscillators and accumulators (especially IMPATT oscillators) have been plagued by "molding" or oscillations under various different operating conditions, such as over normal environmental temperature ranges or a mechanical frequency tuning bandwidth, at frequencies other than the desired oscillation frequency. Numerous patents, such as U.S. Pat. Nos. 3,534,293; 3,628,171; 3,931,587; 3,984,788; 4,016,507; 4,034,314; and 4,075,573, have been directly or indirectly concerned with the problem. Prior art microwave IMPATT oscillators have also exhibited starting problems at low duty factor and/or cold temperatures. Also, prior art microwave IMPATT oscillators and especially IMPATT microwave power accumulators have exhibited a tendency to have very narrow mechanical frequency tuning ranges. Power drop off or moding tended to be severe for just small changes in the operating frequency or temperature. Hence, there is a need for better solutions to these problems.